It is well known in the art that lean fuel/air mixtures may be used advantageously to produce relatively low levels of exhaust emissions and relatively low fuel consumption. However, drivability often suffers when lean mixtures are employed, because mixtures which are slightly "too lean" result in a markedly increased incidence of combustion instability. Combustion instability results in poor drivability and increased emission of hydrocarbons.
A measurement of engine acceleration has been shown to be a reliable source of information regarding combustion instability. Engine acceleration may be measured by monitoring changes in the speed of the engine, or by measuring the motion of the engine. Further, it has been shown that control systems may be constructed which continuously urge the fuel/air mixture leaner, until an indication of "over-leanness" (combustion instability) is detected at which time the mixture is urged richer. However, these systems require the mixture to be over lean for a period of time before the mixture responds to the enrichening.
Control systems for automobile engines must be especially fast and accurate to provide the correct quantities of fuel and air at each moment in time, while the engine experiences rapid changes in throttle position, speed, and load The ability of a control system to quickly adjust its mixture based on changes in operating conditions is characterized as overall system response Therefore, a need exists to minimize the response time for a lean burn mixture control system.